Ballistic mechanism



C. G. HLSCHUH ET AL BALLIS'VKFIC MECHANISM May 12, 1953 2,638,269

Filed Aug. 22, 1942 INVENTORS. CARL G. HOLSCHUH,cmd ID RAM BY DAV s gTHEIR l ATTORNEY Patented May 12, 1953 BALLISTIC MECHANISM Carl G.Holschuh, Huntington, and David Fram,

Brooklyn, N. Y., assignors to The Sperry Corporation, a corporation ofDelaware Application August Z2, 1942, Serial No. 455,968

3 Claims. l

The present invention is related to the art of computing gun sights.

In prior copending application Serial No. 358,382, for ComputingAircraft Gun Sight, filed September 26, 1940, in the names of C. G.Holschuh and O. A. Vielehr and assigned to the same assignee as thepresent invention, there is disclosed a computing gun sight for aircraftwhich is supported directly on and carried by the gun. The gun isdirectly actuated by the gunner, in this case by direct manualactuation, and the gun sight contains a mechanism adapted to compute therequired lead angle between the target orientation and the gunorientation, and to offset the reticle defining the line of sight of thecomputing gun sight by an amount and in a sense corresponding to thislead angle. `The gunner then rotates the gun and sight to maintain theline of sight directed Ytoward the target, whereby the gun isproperlyoriented for directing a projectile toward the target.

In this prior application, however, the computing gun sight was highlysimplied and is useful only under a restricted range of conditions, inorder to decrease weight and simplify construction. Thus, the mechanismis adapted to produce correct lead angles only for a fixed airspeed anda fixed altitude of the craft. For other airspeeds and other altitudes,the lead angle introduced by the mechanism is only approximatelycorrect, so that the utility of the device is somewhat limited. Withrecent types of aircraft, it is necessary to permit wide variations inaltitude and indicated airspeed during actual combat operations in whichthe computing gun sight would be utilized. One method of introducingthese two quantities as variables in the computing mechanism isdisclosed in a similar computing gun sight in copending applicationSerial No. 411,186 for Interaircraft Gun Sight and Computer, filedSeptember 17, 1941, in the names of C. G. Holschuh and D. Fram and alsoassigned to the same assignee as the present application.

In this latter application, a setting control is provided for indicatedairspeed, whereby the apparatus may be set at the actual airspeed of thecraft and so that this airspeed may then be taken into account by themechanism. At the same time, changes in altitude, which have essentiallythe same effect as changes in airspeed of opposite sense, are taken intoconsideration in the mechanism by offsetting the indicated airspeedcontrol by an amount corresponding to the craft altitude as determinedby the relationship for true airspeed which equates this quantity to theproduct of indicated airspeed times a function of the air density ratio.However, in this type of computing mechanism, it is necessary to resolvethe indicated airspeed (which has the same effect as a wind of similarvelocity blowing along the longitudinal axis of the craft) intocomponents along the orientation of the gun, that is, along the path ofthe projectile, and at right angles thereto, in order to isolate thehead wind and cross wind eifects of this relative wind. However, suchresolving mechanisms are cumbersome and awkward to use, introducingdefinite errors and complicating the construction and manufacture of thedevice.

According to the present invention, an aircraft computing gun sight of atype similar to that shown in application 358,382 is provided, whichallows for the effects of changes of altitude and indicated airspeed,and avoids the necessity for the wind resolving mechanisms, such as thatshown in application Serial No. 411,186 and formerly believed to benecessary. In the present invention, it has been found that in place ofutilizing such a wind resolving mechanism, the elevation and azimuthlead angle components ps and respectively due to the effects of relativewind, gravity and projectile spin, may be determined by a particularmethod of mechanical computation in which the azimuth ballisticcorrection is determined as a function of two quantities, one of thesequantities being the actual azimuth component of the gun orientation(Ag) and the other of these quantities being in turn a compositefunction of target slant range (Do) indicated airspeed (IAS) andaltitude (H), this latter composite function being a product of furtherfunctions of these particular quantities individually, as will bedescribed in detail below. The elevation ballistic correction orsuper-elevation 5 may be determined as a function of the gun azimuth(Ag), the gun elevation (Eg) and the same function of slant range (D0)indicated airspeed (IAS), and altitude (H) used in determining theazimuth ballistic correction In addition, the present invention utilizesimproved apparatus for determining the rate of change of target bearingsi. e., angular rate of the gun or sight, and for deriving therefrom thecomponents of the lead angle due to motion of the target during the timeof night of the projectile. For this purpose a pair of rate gyroscopesis used, similar to those disclosed in the patent to Charles S. Draper,2,291,612, for Turn Indicators, dated August-4, 1942, and also incopending applications Serial Nos. 385,916, for Fire Control Apparatus,led March 29, 1941, in the names of C. S. Draper and E. P. Bentley andapplication 440,660 for Lead Computing Devices, led April 27, 1942, inthe names of C. S. Draper and E. P. Bentley. As is shown in theseapplications 385,916 and 440,660, a pair of rate gyroscopes is mountedupon the gun in such fashion that they measure the rates of change oforientation of the gun about the elevation axis and an axis normal tothe slant plane which is defined as a plane including the longitudinaland trunnion axes of the gun. The sensitivity of these rate gyroscopesis then adjusted in accordance with the projectile time of flight,whereby the output derived therefrom represents the product of angulargun rate by time of flight, which is taken to be one predictioncomponent of the required gun lead angle. In the present application,the time of ilight thus utilized for adjusting the rate gyro sensitivityis derived directly from the slant range of the target.

Furthermore, since such gyroscopes are generally airspun from a suitableair pump, and since the output of some pumps varies with altitude, whichwould ordinarily cause a change in rate gyro speed and therefore itssensitivity with altitude, further means may be necessary for adjustingthe output of the air pump in accordance with the altitude to maintainconstant spin velocity for the rate gyros, whereby they are renderedinsensitive to changes in altitude.

Accordingly it is an object of the present invention to provide improvedcomputing gun sights for aircraft adapted to produce improved accuracywith increased simplicity of construction, over a wider range ofconditions of use.

It is another object of the present invention to provide improvedcomputing gun sights for aircraft of the type in which the line of sightdefined by the gun sight is carried by the gun and is also displacedrelatively to the gun by the computing mechanism, and in which theeffect of changes in altitude and changes in airspeed of the craft maybe taken into consideration, whereby the range of use of the device maybe greatly extended and its accuracy improved over prior art devices.

It is a further object of the present invention to provide an improvedcomputing mechanism for inter-aircraft computing gun sights which takesinto consideration the effect of changes in altitude and indicatedairspeed without requiring the use of mechanical resolving mechanisms,

whereby increased simplicity of construction and d higher accuracy maybe obtained.

It is still a further object of the present invention to provideimproved computing gun sights for aircraft utilizing rate gyros forobtaining prediction corrections for the line of sight and wherein thesegyros are compensated for the effects of change in altitude in order torender them useful over all altitudes likely to be encountered.

Other objects and advantages will become apparent as the descriptionproceeds.

The single gure shows a perspective schematic representation of theentire computing gun sight of the present invention. The arrows indicatethe direction of control influences.

It is to be understood that the entire apparatus shown in the figure issuitably mounted upon the gun, in a relationship to be described, andthereby rotates together with the gun both in elevation and azimuth, thegun being suitably 4 controlled either by direct manual control or bymanually-controlled power means.

Also controlled by the operator or gunner is a range control I0 whichactuates a range shaft I I. Shaft II operates through suitable gearingI2 to rotate a three-dimensional cam I3 by means of an elongated pinionI4 and a gear I6 fixed to cam I3. Cam I3 is also axially positioned bymeans of a target dimension control I'I by way of shaft I8, pinion I9,and rack 2I. The follower 22 of cam I3 translates one member 23 of therange-finding reticle, a second member 24 of which is thereby translatedequally and oppositely, by virtue of its opposite connection to lever 25having a fixed pivot as at 26. Member 23 is provided with a slot 21 andmember 24 with a slot 28, through which light rays from a suitablesource of illumination, indicated schematically as a light bulb 29, areprojected onto an azimuth mirror 3|, then reflected into the elevationmirror 32 and thereby to a reflex mirror 33, which serves to superposethis image of the reticle formed by slots 21 and 28 upon the image ofthe object or target. Such a range finder is also shown in copendingapplication Serial No. 358,382.

In operation, target dimension control I'I, which cooperates with asuitable scale 34 and index 36, is set at the known or assumed value ofwing spread of the target. The range control is then actuated by thegunner until the image of slots 21 and 28 as seen through the reflexmirror 33 just circumscribes or outlines the target. This is the desiredtracking condition.

Target dimension dial 34 is calibrated preferably in logarithms oftarget dimension. Cam I3 is so laid out that when positioned intranslation by the target dimension control I1, the displacement ofrange shaft II required to position the cam in rotation to adjust thereticle so as to bracket the target will be proportional to the naturallogarithm of a function of the slant range D0. The function isdetermined empirically for each kind of projectile from ballistic tablesfurnished by the Government.

Preferably, this function of slant range is the ratio of the actualtarget slant range to a predetermined slant range datum.

This angular displacement of slant range shaft I l is then modified bybeing added to other angular displacements made in accordance withlogarithms of functions of altitude and indicated airspeed empiricallydetermined from the ballistic tables for the particular projectile used.Thus, an altitude control knob 31 is provided carrying a scale 38cooperating with a fixed index 39. The scale A38 is so calibrated thatsetting knob 31 to a predetermined altitude, corresponding to the craftaltitude, will rotate altitude shaft 4I through an angle having apredetermined functional relationship to the actual craft altitude. Anexample of one form of functional relationship which has been found tobe satisfactory for a known projectile, is proportional to theexpression:

An indicated airspeed control 42 is also provided having a scale 43cooperating with a fixed index 44 and actuating a shaft 46. The scaleupon indicated airspeed knob 42 is so calibrated that when the mark onscale 43 corresponding to the craft airspeed is set opposite index 44,IAS shaft 46 Will be angularly displaced from a predetermined neutral orzero position by an amount proportional to a predetermined function ofthe craft indicated airspeed. A satisfactory form for this predeterminedfunction has been found to be the following:

1.171 logd for airspeeds between 100 and 200 miles per hour, and

2.7 apa, (awp for airspeeds between 200 and 400 miles per hour.

The angular displacement of shaft 4| is added 1.171 log,%0

This resultant angular displacement of shaft 5| then serves toproportionally rotate a pinion 52 by way of gearing 53, and therebyserves to displace an anti-logarithmic cam 54 by a proportional amount.Cam 54 is rotatably mounted upon a shaft 56 and carries a groove 51cooperating with a follower 58 fixed to the gun or casing of thecomputing gun sight. Thus, as cam 54 is rotated by means of pinion 52,the action of follower 58 in groove 51 serves to axially translate thecam 54. The form of groove 51 on the body of cam 54 is so chosen thatthe axial displacement of cam 54 will be proportional to theanti-logarithm of the angular displacement of the cam 54 produced bypinion 52, and hence to the anti-logarithm of the above combination. Itis to be noted that this axial motion of cam 54 is thus proportional toa product of individual functions of airspeed, altitude and slant range.

Axially translatable with cam 54, but rotated independently thereof, area pair of cams 59 and 60, which are rigidly fixed together and arerotated simultaneously by means of pinion 6| driven from a shaft 62 byway of gearing 63, in accordance with the angular displacement of thegun in azimuth from a predetermined datum which, may be termed gunazimuth Ag. Cams 59 and 6B are ballistic cams which amount to mechanicalballistic tables. The cams in each case are laid out empirically for agiven type of projectile according to well known practice to effectdisplacement of their respective lift pins in accordance with theballistic deflection required for each combination of cam inputdisplacements. In the case of cam 6D, as will be described presently,the displacement of the lift pin thereof is modified by a further cam18. Cam 59 is so designed that the resultant lift of its cam follower 64will be proportional to the azimuth ballistic correction correspondingto the particular values of slant range, gun azimuth, indicatedairspeed, and altitude set into the mechanism in the manner describedfor the 6 particular projectile for which the cam is designed.

This motion of cam follower 64 is then transferred by way of rack 66,pinion 61, shaft 68, pinion 69, rack 10, and arm 1| to rotate lever 12about a pivot 13 (whose position is determined in a manner to bedescribed) and thereby correspondingly actuates an arm 14 pivotallyconnected to a crank 16 fixed to azimuth mirror 3|, and hence mirror 3|is angularly displaced by an angle corresponding to the azimuthballistic correction necessary to compensate for the effect of relativewind (airspeed), and projectile spin upon the path of the projectile.

The follower 11 of the second cam 60 serves to axially position afurther cam 18, which is rotated by means of pinion 19 from shaft 8|through gearing 82 in accordance with the elevational angulardisplacement (Eg) of the gun from a predetermined datum. Cams 60 and 18are so designed that the resultant lift of cam follower 83 of cam 18will be the super-elevation correction qss.

In accordance with a feature of the invention,

D0 H H 2 loge 10g,

the effect on the projectile of the air speed of the plane together withthe density of the air, the azimuth angle of the gun, and slant range ofthe target are taken into consideration along with the changingelevation angle of the gun and a correction for gravity in computingvertical ballistic deflection.

Cam 6U is laid out to compute for a predetermined constant gun elevationangle, the vertical ballistic deection required for the particularcombination of variables by which the cam is displaced. Lift pin 11accordingly translates cam 18 according to this ballistic data forconstant gun elevation. Cam 18 is rotated in accordance With thechanging gun elevation angle. The cam is laid out empirically to correctthe data from cam 60 in accordance with changing gun elevation. Includedin the data on the cam surface is a correction for gravity, the lift pin83 being displaced in accordance with the vertical ballistic deflection.

This lift of follower 83 is then transferred by way of rack 84, pinion85, shaft 86, gearing 81, shaft 88, gearing 89, shaft 9|, and crank 92fixed to shaft 9|, to a pivotally-connected link 93 which operates acrank arm 94 pivoted about a shaft 96. Motion of crank 94 about shaft 96correspondingly displaces a link 91 pivoted to a crank 98 fastened tothe pivot axis of mirror 32, and thereby angularly displaces mirror 32through an angle corresponding to the superelevation correction fps.

In addition to the ballistic corrections and 0g required between theorientations of the target and the gun, an additional predictioncorrection in azimuth and elevation must be supplied to allow for themotion of the target during the time of flight of a projectile. Thiscorrection in the present instance is supplied by the respective azimuthand elevation rate gyros 99 and IUI.

These gyros are mounted on the gun in such manner that the spin axis ofthe azimuth gyro 99 is parallel to the elevation trunnion axis of thegun and the spin axis of the elevationrate gyro is perpendicular to theslant plane containing the elevation gun trunnion axis and thelongitudinal axis of the gun. These gyros are preferably of the typeshown in above-mentioned copending application Serial No. 440,660,wherein the angular displacement of their respective output arms |02 and|03 from predetermined respective datum positions is proportional to theangular velocity of the gyro mount about axes perpendicular to theirrespective spin axes.

In the case of the azimuth gyro 99, this rate is measured about an axisperpendicular to the slant plane containing the elevation trunnion axisand the longitudinal axis of the gun, and hence measures the gun slantpant azimuth rate. In the case of the elevation rate gyro |0|, this rateis measured about the elevation trunnion axis of the gun, and determinesthe gun elevation rate.

As described in the above-mentioned application Serial No. 440,660, thesensitivity of these gyros, namely, their output angular displacementsfor a predetermined impressed angular velocity, may be suitablyadjusted, as by adjustment of control members |04 and |05. In thepresent case, this sensitivity is adjusted in proportion to the time offlight T of the projectile, whereby the output angular displacements ofcranks |02 and |03 are respectively proportional to time of flight Ttimes the angular velocity of the gun in slant plane azimuth and inelevation, respectively. These quantities may be termed, respectively,the slant plane azimuth prediction correction, and the elevationprediction correction.

For this purpose, shaft which, as has been described, is rotated inaccordance with a predetermined logarithmic function of slant range Do,is connected through gearing |06, shaft |01, gearing |08, and shaft |09to a cylindrical cam whose follower ||2 is connected to racks ||3 and||4, respectively engaging gears formed on or connected to sensitivitycontrol members |04 and |05. As is known, the time of flight T of aprojectile to a close order of accuracy is a function solely of slantrange Do, al1 other variables being resolved in the determination. Camis a delogging cam and has its groove l0 so formed that thetranslational displacement of racks ||3 and ||4 in response to theangular displacement of slant range control shaft will be in proportionto the time of ilight T corresponding to the slant range Do determiningthe displacement of shaft The angular displacement of crank |02,proportional to the azimuth prediction correction, is then transmited byway of a pivoted link IIB, a crank |1 pivoted about shaft ||8 and xed tocrank ||9, and a pivoted link |2| to lever |22, which is pivoted aboutan axis |23 fixed to the instrument housing. Lever |22 is also rigidlyconnected to pivot axis 13, already described.

It will be seen that arm 1I is determined as to position by theapparatus already described. Accordingly, any displacement of lever |22about axis |23 must result in a motion of pivot axis 13 and crank 12about the pivot joining crank 12 and arm 1|. This results in a furthercomponent of motion of arm 14 corresponding -to the azimuth predictioncorrection, so that the mirror 3| is angularly displaced by the sum ofthe slant plane azimuth prediction and ballistic corrections, whichamount to the entire slant plane azimuth lead angle. In eiect,therefore, crank 8 12, lever |22, and pivot 13 form a, mechanical leverdifferential Whose output, derived from arm 14, represents the sum ofthe inputs to arms |2| and 1|.

In similar fashion, the elevation prediction correction is led by way oflink |24 and crank |25 to a similar lever differential and thereby alsorotates the elevation mirror 32, which is thus angularly displaced inaccordance with the elevation lead angle equal to the sum of theelevation prediction correction and the super-elevation correction.

Since mirrors 3| and 32 are carried by the gun, it will be seen that theresultant displacement produced in the reticle image will correspondboth in magnitude and sense to the lead angle which the gun must bearwith respect to the line of sight of the target. The system is soadjusted that for zero prediction and ballistic corrections, the line ofsight dened by the reticle will coincide with the gun orientation.Accordingly, when a target is tracked so that its image is maintainedcentralized between the vertical arms of the reticle image formed byslots 21 and 28, the target orientation thus dened will be displacedfrom the gun orientation by the amount of the proper lead angle and,accordingly, under these circumstances, the gun will be exactly orientedfor properly directing the projectile red from the gun. In this way, asimple and accurate computing gun sight adapted to be used over a widerange of variation of gun orientations approximating a completehemisphere is provided.

Gyros 99 and |0| are preferably air spun by means of a suitable air pump3| connected to the respective gyros 99, |0| by respective air ducts |32and |33, in the manner shown in application Serial No. 440,660. Theoutput deflection from rate gyros of the present type is trulyproportional to the angular velocity impressed thereon only when theyare maintaining constant spin velocity. Normally, as the craft changesaltitude, resulting in a variation in air density, the output from apump such as |3| would vary in accordance with the altitude, therebyvarying the spin velocity of the gyros. To prevent this, according tothe present invention, the pump rate is adjusted in correspondence withthe altitude of the craft to maintain constant spin velocity of thegyros. This is done in the present instance by utilizing a variableoutput pump having a control member |34 which is adapted to vary theoutput in ducts |32 and |33. Such pumps are wellknown and their detailsform no part of the present invention.

Connected to altitude control 31, as by way of gearing |36 and shaft|31, is a cam |38, whose follower |39 is connected to a rack |4|cooperating with a pinion |42 connected to the pump control |34. Thegroove |40 of cam |38 is so formed that the spin velocities of gyros 99and |0| will remain constant so long as the altitude set in by means ofcontrol 31 corresponds to the actual altitude of the craft. In this way,errors due to change in altitude which would otherwise be encountered,are prevented.

It will be clear that the above type of prediction lead angledetermining apparatus need not be restricted to use directly on the gun,but may be mounted on a dummy gun or a sight.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof,

it is intended that all matter contained in the above description orshown in the accompanying drawings shall be interpreted as illustrativeand not in a limiting sense.

What is claimed is:

1. In a ballistic computer for airborne ordnance, a plurality ofmanually adjustable knobs having individual logarithmic dials,differential means actuated by said knobs according to logarithms ofpredetermined functions of altitude and air speed of the supportingaircraft and slant range of a target, anti-logarithm means actuated bythe output of the differential means for providing a linear outputdisplacement proportional to the product of said functions,threedimension ballistic cam means displaced in one dimension by theoutput of the anti-logarithm means and in another dimension according togun azimuth, the ballistic cam means being laid out to provide outputballistic deflections according to magnitude of the displacementsimparted to the cam.

2. In a ballistic computer for airborne ordnance, a plurality ofmanually adjustable knobs having individual logarithmic dials,differential means actuated by the knobs according to logarithms ofpredetermined functions of altitude and air speed of the supportingaircraft and slant range of a target, an anti-logarithm cam memberdisplaced by the output of the diierential means in accordance With thesum of the logarithms of said functions for producing an outputdisplacement proportional to the product of said functions, ballisticcam means comprising a pair of ballistic cams displaced on one dimensionby the output of the anti-logarithmic cam member, and in anotherdimension accor-ding to gun azimuth, the ballistic cams being laid outrespectively to provide output displacements in accordance with thelateral ballistic deection, and the vertical ballistic deiiection, thelatter being based on some predetermined constant gun elevation.

3. In a ballistic computer for airborne ordnance, a plurality ofmanually adjustable knobs having individual logarithmic dials,differential 10 means actuated by the knobs according to logarithms ofpredetermined functions of altitude and air speed of the supportingaircraft and slant range of a target, an anti-logarithm cam memberdisplaced by the output of the differential means in accordance with thesum of the logarithms of said functions for producing an outputdisplacement proportional to the product of said functions, a pair ofballistic cams fixed to each other displaced in one dimension by theoutput of the anti-logarithm cam member, and in another dimensionaccording to gun azimuth, one ballistic cam being laid out to provide anoutput displacement according to lateral ballistic deection, and theother to provide a displacement according to vertical ballistic deectionat constant gun elevation, and means comprising a further cam displacedin one dimension by the latter ballistic cam and in another dimensionaccording to gun elevation for providing vertical ballistic deflectioncorrected for gun elevation.

CARL G. HOLSCHUH.

DAVID FRAM.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,291,031 Leavitt Jan. 14, 1919 1,482,152 Ross Jan. 29, 19241,801,329 Carter et al. Apr. 21, 1931 2,065,303 Chafee et al. Dec. 22,1936 2,133,489 Smith Oct. 18, 1938 2,175,143 Cornelius Oct. 3, 19392,206,875 Chafee et al. July 9, 1940 2,235,826 Chafee Mar. 25, 19412,248,141 Von Manteuffel July 8, 1941 2,385,348 Chafee Sept. 24, 19452,396,701 I-Iolschuh Mar. 19, 1946 FOREIGN PATENTS Number Country Date499,265 Great Britain Jan. 20, 1939 OTHER REFERENCES Ser. No. 212,349,Papello (A. P. (2.), published May 25, 1943.

